msm: pm-8x60: Remove unused API msm_pm_set_max_sleep_time()

msm_pm_set_max_sleep_time() was used by rtc drivers to wake a system up
from suspend on targets that doesn't have a RTC hardware. The targets
that invoke pm-8x60 has dedicated rtc drivers and can rely them for
wakeup from suspend.

While at it also remove the max sleep limit imposed during idle sleep.
The code seems to have been ported over from older targets but the
targets with these limitations aren't supported by the pm-8x60 file.

Change-Id: I03a78f226b50aa24504537c81b9fc7fa00eca883
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>